The upstream oxygen sensor is mounted in the exhaust manifold The downstream oxygen sensor is mountedin the exhaust pipe after catalytic converter.
The oxygen sensor is in the exhaust system.It aids the exhaust gas recirculation (EGR) valve to send unburned gases back through for reburn. For cleaner exhaust. The oxygen sensor is at fault.
The sensor may also fail in a lean mode, which would produce low emissions but slightly lean running, so that engine operation would be just slightly rough. The sensor should be replaced at the correct maintenance interval for that year and model (refer to the maintenance intervals chart) as a matter of routine maintenance.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.